OBSERVATIONS ON THE MECHANISM OF HALOGEN-BRIDGE CLEAVAGE BY UNIDENTATE LIGANDS IN SQUARE-PLANAR PALLADIUM AND PLATINUM COMPLEXES

Cyclo-palladation and -platination of nitrogen donor ligands lead to i nsoluble mu-chloro dimers which give mu-bromo and mu-iodo dimers on me tathesis with the appropriate lithium halide. Addition of pyridine or 2,6-dimethylpyridine to the cyclopalladated dimers gives monomeric com plexes with the halogen trans to the metal-carbon bond, whereas additi on of 2,6-dimethylpyridine to the cycloplatinated complexes gives the isomer with the halogen cis to the metal-carbon bond. The results are discussed in terms of the mechanism of the bridge cleavage reaction.